There is known a heat pump type hot water supply apparatus that generally has a refrigerating cycle including a compressor, a gas cooler, a pressure reducing device and an evaporator and is designed to supply water heated by the gas cooler.
This type of apparatus has hitherto used freon containing chlorine (HCFC22 or the like) as refrigerant in a refrigerating cycle. However, from the viewpoint of ozone layer protection, restriction of use of freon has been promoted. Even in the case of freon containing no chlorine (HFC) as substitute refrigerant, it has been specified as a restriction target material in Kyoto Conference on Global Warming (COP3) because it has a high global warming potential.
Therefore, a motion of using materials existing in the natural world in place of synthetic material such as freon as refrigerant in the refrigerating cycle has been promoted, and particularly use of CO2 refrigerant in the refrigerating cycle has been promoted to be considered.
When CO2 refrigerant is used, a transcritical cycle in which the high-pressure side of the refrigerating cycle is transformed into a supercritical state is established, and thus it is expected that a high coefficient of performance (COP) can be achieved in a heating process having a large water-temperature rise-up range as in the case of hot water supply by a heat pump type hot water supply apparatus.
However, at the same time, the refrigerant must be compressed to a high pressure, so that an internal intermediate pressure two-stage compression type compressor has been recently used.
In this type of apparatus, devices constituting the refrigerating cycle are frequently disposed as a heat pump unit outdoors, and for example in a winter season or the like, it is frequently required to carry out the defrosting operation on an evaporator.
In this case, it is general to perform a hot gas defrosting operation in which refrigerant discharged from the compressor is supplied to the evaporator with bypassing the gas cooler and the pressure reducing device so that the evaporator is heated with the heat of the refrigerant to be defrosted. However, any defrosting circuit to be used when a two-stage compression type compressor is used has not yet been proposed.
Therefore, an object of the present invention is to solve the problem of the prior art and provide a heat pump apparatus which can perform a defrosting operation efficiently when a two-stage compression type compressor is used.